Recipients print a coupon with a bar code that includes the account number, and mail it in with a check.

WSJ: For Graduation, a Gift of a 529

Dr. SKRAPEC SYNC: Right now if there is a criminal like a serial killer or bank robber, they are able to print in the code, 'cos each face you make has a particular code, a number for the eyebrows and a number for the nostril.

BBC